JP7839963B2 - Catalyst layer of fuel cell and fuel cell - Google Patents

Description

This disclosure relates to a catalyst layer for a fuel cell and a fuel cell.

Patent Document 1 discloses a technology capable of more efficiently discharging moisture from the catalyst layer and suppressing flooding in a fuel cell. This fuel cell comprises an electrolyte membrane, a catalyst layer formed on the surface of the electrolyte membrane, and a gas diffusion layer formed on the surface of the catalyst layer opposite the electrolyte membrane.

This catalyst layer comprises a proton-conducting ionomer, a catalyst support covered at least partially by the ionomer, and pores within the catalyst layer extending from the gas diffusion layer towards the electrolyte membrane. The cross-sectional area of the pores in the direction in which the electrolyte membrane, catalyst layer, and gas diffusion layer are stacked is larger on the gas diffusion layer side of the catalyst layer than on the electrolyte membrane side.

Japanese Patent Publication No. 2013-145652

This disclosure provides a catalyst layer for a fuel cell that achieves both high conductivity and excellent drainage, thereby providing highly efficient power generation performance.

The catalyst layer in this disclosure is a catalyst layer interposed between the gas diffusion layer and the electrolyte membrane of a fuel cell, and this catalyst layer comprises a first catalyst layer adjacent to the gas diffusion layer and a second catalyst layer adjacent to the electrolyte membrane.

The first catalyst layer and the second catalyst layer each include a first conductive material, a second conductive material having a smaller mode diameter compared to the first conductive material, and a catalyst supported on at least one of the first and second conductive materials.

Furthermore, the first catalyst layer is characterized by having a smaller proportion of the weight of the second conductive material relative to the total weight of the first and second conductive materials compared to the second catalyst layer.

The catalyst layer in this disclosure can improve the drainage properties of the catalyst layer while suppressing the decrease in electrical conductivity caused by a reduction in the contact area between conductive materials. Therefore, using the catalyst layer in this disclosure in a fuel cell can improve the power generation performance of the fuel cell.

A schematic diagram showing the general cross-sectional configuration of the fuel cell cell in Embodiment 1. A schematic diagram showing the general configuration of the cross-section of the catalyst layer in Embodiment 1. A schematic diagram illustrating the capillary pressure acting on water within a void where the void diameter increases as the direction of movement increases. Schematic diagram to explain a close-packed sphere structure. Schematic diagram illustrating the positional relationship between the mesoporous material and the ionomer in the catalyst layer in Embodiment 1.

(Knowledge and other information that formed the basis of this disclosure)
At the time the inventors conceived of this disclosure, fuel cells were attracting attention as a key device necessary for realizing a decarbonized society because they generate electricity by reacting hydrogen and oxygen and produce only water during the power generation process.

To improve the power generation efficiency of fuel cells, it is necessary to efficiently discharge the water produced during the power generation reaction, allowing the reaction gases, oxygen and hydrogen, to reach the catalyst point without obstruction.

To facilitate the discharge of the generated water, the system utilizes the property that water within pores is pushed from the smaller diameter pore to the larger diameter pore due to capillary pressure. This configuration promotes drainage from the catalyst layer with smaller pore diameters towards the gas diffusion layer and separator with larger pore diameters.

However, since the pore size distribution within the catalyst layer is approximately constant, it has become clear that the accumulation of generated water within the catalyst layer inhibits gas diffusion, contributing to a decrease in power generation performance.

To further improve power generation performance, it was necessary to further enhance the drainage within the catalyst layer. This led to the idea of creating a distribution within the catalyst layer where the pore diameter increases from the electrolyte membrane side towards the gas diffusion layer side.

However, the inventors discovered that when a single catalyst-supporting material is laminated and the gap diameter is controlled by the density of the lamination, the contact area between the catalyst-supporting materials decreases in regions with large gap diameters, resulting in reduced conductivity. This makes it difficult to achieve both excellent drainage and high conductivity simultaneously. To solve this problem, the subject matter of this disclosure was established.

Therefore, this disclosure provides a catalyst layer and fuel cell that improve power generation efficiency in fuel cells by achieving both excellent drainage and high conductivity.

The embodiments will be described in detail below with reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

The attached drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
Embodiment 1 will be described below with reference to Figures 1 to 5.

[1-1. Structure]
(fuel cell)
Figure 1 shows an example of the configuration of a fuel cell cell, which is the basic unit of a fuel cell. The fuel cell cell 7 shown in Figure 1 is a solid polymer electrolyte fuel cell that generates electricity by reacting hydrogen supplied to the anode with oxygen supplied to the cathode.

As shown in Figure 1, the fuel cell cell 7 has an electrolyte membrane-electrode assembly 6 between the anode separator 5a and the cathode separator 5c.

The anode separator 5a has a channel on the surface in contact with the anode 2a of the electrolyte membrane-electrode assembly 6 that allows hydrogen supplied to the fuel cell cell 7 to flow to the anode 2a of the electrolyte membrane-electrode assembly 6.

The cathode separator 5c has a channel on the surface in contact with the cathode 2c of the electrolyte membrane-electrode assembly 6 that allows oxygen supplied to the fuel cell cell 7 to flow to the cathode 2c of the electrolyte membrane-electrode assembly 6.

If the fuel cell cell 7 has a stacked structure, the adjacent anode separator 5a and cathode separator 5c electrically connect the adjacent cells.

The electrolyte membrane-electrode assembly 6 comprises an electrolyte membrane 1, an anode (fuel electrode) 2a including an anode catalyst layer 3a and an anode gas diffusion layer 4a, and a cathode (air electrode) 2c including a cathode catalyst layer 3c and a cathode gas diffusion layer 4c. The electrolyte membrane 1 is sandwiched between the anode 2a and the cathode 2c.

(electrolyte membrane)
The electrolyte membrane 1 facilitates ion conduction between the anode 2a and the cathode 2c, and therefore needs to possess both ionic conductivity and gas barrier properties. In this embodiment, a perfluorosulfonic acid resin membrane was used as the electrolyte membrane 1. This perfluorosulfonic acid resin membrane is preferable because it has high hydrogen ion conductivity and remains stable even under the power generation environment of a fuel cell.

(Gas diffusion layer)
The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c are layers that possess current collection properties, gas permeability, and water repellency. The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c may also consist of two layers: a substrate and a coating layer.

The substrate can be any material with excellent conductivity and permeability to gases and liquids. In this embodiment, carbon paper was used as the substrate.

The coating layer is interposed between the substrate and the catalyst layer (anode catalyst layer 3a or cathode catalyst layer 3c) to reduce contact resistance and improve liquid permeability (drainage). In this embodiment, the coating layer was formed primarily from a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE).

(catalyst layer)
The anode catalyst layer 3a and the cathode catalyst layer 3c are layers that promote the electrochemical reaction between the anode 2a and the cathode 2c.

The catalyst layers of the anode catalyst layer 3a and the cathode catalyst layer 3c include a conductive material, a catalyst supported on the conductive material, and an ionomer (hydrogen ion conductive resin) that covers at least a portion of the conductive material.

As shown in Figure 2, the cathode catalyst layer 3c has a first catalyst layer 11a adjacent to the cathode gas diffusion layer 4c and a second catalyst layer 11b adjacent to the electrolyte membrane 1.

The first catalyst layer 11a and the second catalyst layer 11b each consist of the first conductive material 10a and,
It consists of a second conductive material 10b having a smaller mode diameter compared to the first conductive material 10a, a catalyst 12 supported on at least one of the first conductive material 10a and the second conductive material 10b, and an ionomer 13 covering at least a portion of the first conductive material 10a and the second conductive material 10b.

Furthermore, the first catalyst layer 11a has a smaller ratio X of the weight of the second conductive material 10b to the total weight of the first conductive material 10a and the second conductive material 10b compared to the second catalyst layer 11b.

In this embodiment, to suppress the decrease in conductivity due to a reduction in the contact area between conductive materials, the ratio X in the first catalyst layer 11a was 0.05. Furthermore, to improve gas diffusion by reducing the thickness of the cathode catalyst layer 3c, the ratio X in the second catalyst layer 11b was 0.3.

(Conductive materials)
In this embodiment, a mesoporous carbon with a mode diameter of approximately 500 nm was used as the first conductive material 10a, and carbon black with a mode diameter of 50 nm was used as the second conductive material 10b. In this embodiment, the mode diameter of the second conductive material 10b was 10% of the mode diameter of the first conductive material 10a.

(catalyst)
As shown in Figure 2, the catalyst 12 is supported on at least the first conductive material 10a of the first conductive material 10a and the second conductive material 10b. In this embodiment, a platinum-containing alloy was used as the catalyst 12. The mode diameter of the catalyst 12 was 5 nm.

(Ionoma)
As shown in Figure 2, the ionomer 13 is a polymer with hydrogen ion (H ⁺ ) conductivity and coats at least a portion of the first conductive material 10a and the second conductive material 10b. In this embodiment, a perfluorosulfonic acid polymer with high hydrogen ion conductivity and stable presence even under the power generation environment of a fuel cell was used as the ionomer 13.

(Mesoporous material)
In this embodiment, the first conductive material 10a used was the mesoporous material 14 shown in Figure 5, and mesoporous carbon was used as the mesoporous material 14. Before supporting the catalyst 12, the mode diameter of the mesopores 15 of the mesoporous material 14 was 10 nm, and the pore volume of the mesopores 15 was 2.0 ^cm³ /g. The mode diameter of the mesoporous material 14 was 500 nm.

[1-2. Operation]
Based on Figure 1, the operation method and function of the fuel cell cell 7 will be explained. The temperature of the fuel cell cell 7 is set (maintained) to 60°C, hydrogen with a dew point of 60°C is supplied to the flow path of the anode separator 5a at a flow rate of 100 cc/min, and air with a dew point of 60°C is supplied to the cathode separator 5c at a flow rate of 300 cc/min, causing a current of 10A to flow through the external circuit connecting the anode 2a and cathode 2c.

Next, we will explain the movement of substances and electrochemical reactions within the electrochemical device during operation. Hydrogen supplied to the flow path of the anode separator 5a passes through the anode gas diffusion layer 4a and reaches the catalyst in the anode catalyst layer 3a.

In the anode catalyst layer 3a, an oxidation reaction occurs in which hydrogen dissociates into hydrogen ions (H ⁺ ) and electrons, as shown in (Chemical Formula 1). The hydrogen ions (H ⁺ ) pass through the anode catalyst layer 3a (ionomer), conduct through the electrolyte membrane 1, and reach the catalyst 12 in the cathode catalyst layer 3c.

Electrons dissociated in the anode catalyst layer 3a pass through the anode catalyst layer 3a, the anode gas diffusion layer 4a, and the anode separator 5a, then through the power lines and electronic load device, and finally through the cathode separator 5c, the cathode gas diffusion layer 4c, and the cathode catalyst layer 3c, reaching the catalyst 12 in the cathode catalyst layer 3c.

Oxygen in the air supplied to the flow path of the cathode separator 5c passes through the cathode gas diffusion layer 4c and reaches the catalyst 12 in the cathode catalyst layer 3c. In the cathode catalyst layer 3c, a reduction reaction occurs in which hydrogen ions (H ⁺ ), oxygen (O), and electrons combine to produce water, as shown in (Chemical Formula 2).

To improve the power generation performance of the fuel cell cell 7, it is necessary for the raw materials, hydrogen and oxygen, to efficiently reach the anode catalyst layer 3a and cathode catalyst layer 3c, respectively. However, since the water generated during the power generation reaction inhibits gas diffusion in the cathode catalyst layer 3c, it is necessary for the water to be efficiently discharged from the cathode catalyst layer 3c through the cathode gas diffusion layer 4c into the flow path of the cathode separator 5c.

As shown in Figure 2, the cathode catalyst layer 3c has a smaller mode diameter of the pore on the electrolyte membrane 1 side than on the cathode gas diffusion layer 4c side. The magnitude of the capillary pressure acting at the gas-liquid interface of water accumulated in the pore follows the Young-Laplace equation shown in (Equation 1) and is proportional to the reciprocal of the pore diameter.

Therefore, as shown in Figure 3, the capillary pressure P1 on the surface with a small gap diameter is greater than the capillary pressure P2 on the surface with a large gap diameter. This forces the water accumulated in the gaps within the cathode catalyst layer 3c to be pushed from the electrolyte membrane 1 side towards the cathode gas diffusion layer 4c side, thus improving drainage. Furthermore, increasing the contact area between the conductive materials improves conductivity.

As shown in Figure 4, when spheres a of radius r are packed tightly in a hexagonal pattern, connecting the centers of four adjacent spheres a forms a regular tetrahedron with side length 2r. The distance between the centroid of the regular tetrahedron and its vertices is calculated to be approximately 1.22r. Therefore, the maximum radius of a sphere that can be placed in the gap between four adjacent spheres a when spheres a of radius r are packed tightly in a hexagonal pattern is approximately 0.22r.

Therefore, when the mode diameter of the second conductive material 10b is 22% or less of the mode diameter of the first conductive material 10a, the second conductive material 10b can be placed in the gaps created between the hexagonally close-packed first conductive material 10a, and the mode diameter of the gaps becomes smaller.

When the mode diameter of the voids within the cathode catalyst layer 3c decreases, the difference in mode diameter between the cathode catalyst layer 3c and the cathode gas diffusion layer 4c increases. This increases the force of capillary pressure that expels water from the cathode catalyst layer 3c to the cathode gas diffusion layer 4c, thereby improving drainage. Furthermore, the increased contact area between the conductive materials improves the conductivity of the cathode catalyst layer 3c.

If the first conductive material 10a is a mesoporous material 14 having mesopores 15 internally, and the catalyst 12 is supported within the mesopores 15, then contact between the ionomer 13 and the catalyst 12 within the mesopores 15 can be suppressed.

Since the mode diameter of the shortest side of the ionomer 13 is 50 nm or more, if the catalyst 12 is supported in a mesopore 15 with a smaller diameter, the ionomer 13 cannot enter the mesopore 15, thus suppressing contact. It is known that catalytic activity decreases when the catalyst 12 and ionomer 13 come into contact, but this decrease in activity can be suppressed by suppressing contact.

If the first conductive material 10a or the second conductive material 10b is a carbon-based material, the drainage performance of the cathode catalyst layer 3c is improved. Carbon materials are highly hydrophobic among conductive materials, and can improve the drainage performance of the cathode catalyst layer 3c.

[1-3. Effects, etc.]
As described above, in this embodiment, the cathode catalyst layer 3c has a first catalyst layer 11a adjacent to the cathode gas diffusion layer 4c and a second catalyst layer 11b adjacent to the electrolyte membrane 1.

The first catalyst layer 11a and the second catalyst layer 11b each include a first conductive material 10a, a second conductive material 10b having a smaller mode diameter compared to the first conductive material 10a, and a catalyst 12 supported on at least one of the first conductive material 10a and the second conductive material 10b.

Furthermore, the first catalyst layer 11a is characterized by having a smaller proportion of the weight of the second conductive material 10b relative to the total weight of the first conductive material 10a and the second conductive material 10b compared to the second catalyst layer 11b.

As a result, in the cathode catalyst layer 3c, the second catalyst layer 11b adjacent to the electrolyte membrane 1 has a smaller gap mode diameter between conductive materials than the first catalyst layer 11a adjacent to the cathode gas diffusion layer 4c. This improves drainage because the water generated in the cathode catalyst layer 3c during power generation is pushed outwards by capillary pressure from the electrolyte membrane 1 side towards the cathode gas diffusion layer 4c side.

Furthermore, increasing the contact area between conductive materials can improve conductivity. This allows for the creation of a highly efficient catalyst layer.

Furthermore, as in this embodiment, the cathode catalyst layer 3c may have a mode diameter of the second conductive material 10b that is 22% or less of the mode diameter of the first conductive material 10a.

With this configuration, the second conductive material 10b can be placed in the gap between the first conductive material 10a. Furthermore, by reducing the gap between the conductive materials in the cathode catalyst layer 3c, the difference in mode diameter between the cathode catalyst layer 3c and the cathode gas diffusion layer 4c increases, thereby improving drainage. As a result, a highly efficient catalyst layer can be obtained.

Furthermore, as in this embodiment, the first conductive material 10a of the cathode catalyst layer 3c may be a mesoporous material in which at least a portion is coated with an ionomer 13, and which has mesopores 15 with a mode diameter of 1 to 50 nm inside, with the catalyst 12 supported within these mesopores 15.

With this configuration, contact between the ionomer 13, which has a mode diameter of several tens of nanometers, and the catalyst 12 supported within the mesopores is suppressed, thereby preventing a decrease in catalytic activity due to contact and enabling the acquisition of a highly efficient catalyst layer.

Furthermore, as in this embodiment, the second conductive material 10b of the cathode catalyst layer 3c may be a carbon material.

By configuring it in this way, carbon-based materials, among conductive materials, possess high hydrophobicity, which can further improve the drainage of the cathode catalyst layer 3c, thereby obtaining a highly efficient cathode catalyst layer 3c.

Furthermore, as in this embodiment, the fuel cell cell 7 may be constructed using the cathode catalyst layer 3c of this embodiment.

With this configuration, the drainage and conductivity of the cathode catalyst layer 3c are improved compared to conventional cathode catalyst layers, thereby improving the power generation performance of the fuel cell cell 7.

(Other embodiments)
As described above, Embodiment 1 was explained as an example of the technology disclosed in this question. However, the technology in this disclosure is not limited to this and can be applied to embodiments that have been modified, replaced, or added. Furthermore, it is possible to create new embodiments by combining the components described in Embodiment 1 above.

Therefore, other embodiments are illustrated below.

In Embodiment 1, a perfluorosulfonic acid resin membrane was described as an example of the electrolyte membrane 1. The electrolyte membrane 1 facilitates ion (hydrogen ion) conduction between the anode 2a and cathode 2c, and only requires that it possesses both hydrogen ion conductivity and gas barrier properties. Therefore, the electrolyte membrane 1 is not limited to a perfluorosulfonic acid resin membrane.

The electrolyte membrane 1 is exemplified by, for example, an ion-exchangeable fluorine-based resin membrane or an ion-exchangeable hydrocarbon-based resin membrane. The ion exchange capacity of the ion-exchange resin is preferably 0.9 to 2.0 milliequivalents/g dry resin.

A ion exchange capacity of 0.9 mm equivalent/g dry resin or higher is preferable because it facilitates obtaining high hydrogen ion conductivity, while a ion exchange capacity of 2.0 mm equivalent/g dry resin or lower is preferable because it suppresses swelling of the resin due to water content and reduces dimensional changes in the electrolyte membrane 1.

Furthermore, the thickness of the electrolyte membrane 1 is preferably 5 μm or more and 50 μm or less. A thickness of 5 μm or more provides high gas barrier properties, while a thickness of 50 μm or less provides high hydrogen ion conductivity.

In Embodiment 1, as an example of the anode gas diffusion layer 4a and cathode gas diffusion layer 4c, the structure includes two layers: a substrate and a coating layer. Carbon paper was used as the substrate. The substrate can be any material with excellent conductivity and gas and liquid permeability. Therefore, the substrate is not limited to carbon paper.

Examples of substrate materials other than carbon paper include porous materials such as carbon fiber cloth and carbon fiber felt.

In Embodiment 1, the ratio X of the weight of the second conductive material 10b to the total weight of the first conductive material 10a and the second conductive material 10b was 0.05 in the first catalyst layer 11a and 0.3 in the second catalyst layer 11b. Similar effects are obtained when the ratio X in the first catalyst layer 11a is 0.01 or higher and the ratio X in the second catalyst layer 11b is 0.9 or lower.

In Embodiment 1, mesoporous carbon was used as the first conductive material 10a and carbon black was used as the second conductive material 10b, but the invention is not limited to these.

Examples of materials for the first conductive material 10a and the second conductive material 10b include carbon-based materials such as Ketjenblack (registered trademark), acetylene black, and Vulcan (registered trademark), metallic materials such as Au and Ni, metal oxide materials such as titanium, tin, niobium, tantalum, zirconium, aluminum, and silicon, and composite materials thereof.

When a mesoporous material is used as the first conductive material 10a, the mode diameter of the mesopores 15 may be 1 to 50 nm and the pore volume of the mesopores 15 may be 1.0 to 3.0 ^cm³ /g before the catalyst 12 is supported on the mesoporous material.

If the pore volume of the mesopores 15 is 1.0 ^cm³ /g or more, a large amount of catalyst 12 can be supported inside the mesoporous material, and if it is 3.0 ^cm³ /g or less, the structural strength of the mesoporous material increases.

Furthermore, the mesoporous material may be configured such that its mode diameter is 200 to 1000 nm. If the mode diameter is 200 nm or greater, the region in which the ionomer 13 penetrates the mesopore 15 becomes smaller relative to the pore volume of the mesopore 15, thus reducing the proportion of the catalyst 12 affected by poisoning from the ionomer 13.

Therefore, it is believed that catalytic activity can be improved by setting the mode diameter to 200 nm or more. Furthermore, if the mode diameter is 1000 nm or less, the reaction gas is more easily supplied to the catalyst supported within the mesoporous material.

In Embodiment 1, a platinum-containing alloy was used as an example of catalyst 12. Catalyst 12 is not particularly limited as long as it has catalytic activity for hydrogen gas or oxygen gas.

Examples of materials for the catalyst 12 include metals such as platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), osmium (Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium (Ga), and aluminum (Al), as well as mixtures and alloys of these metals. However, from the viewpoint of improving catalytic activity, toxicity to carbon monoxide, heat resistance, etc., platinum, a mixture containing platinum, or an alloy is preferred.

When the catalyst 12 is made of an alloy, the composition of the alloy depends on the type of metals being alloyed, but the platinum content can be 30 to 90 atomic percent, and the content of other metals can be 10 to 70 atomic percent. The mode diameter of the catalyst 12 is not particularly limited, but from the viewpoint of improving catalyst utilization and supportability in the catalyst-supporting material, it is preferably 1 to 30 nm. When supported in the mesopores 15 of a mesoporous material, a mode diameter smaller than the mode diameter of the mesopores is preferable.

In Embodiment 1, a fuel cell cell 7 was described in which the electrolyte membrane 1 was a hydrogen ion conductive membrane and the catalyst layer of this disclosure was used as the cathode catalyst layer 3c. However, in a fuel cell cell using a hydroxide ion conductive membrane as the electrolyte membrane, it is preferable to use the catalyst layer of this disclosure as the anode catalyst layer.

In a fuel cell using a hydroxide ion conductive membrane as the electrolyte membrane, the reaction shown in (Chemical Formula 3) occurs in the anode catalyst layer to which hydrogen is supplied, and the reaction shown in (Chemical Formula 4) occurs in the cathode catalyst layer to which oxygen is supplied.

In fuel cell cells using a hydroxide ion conductive membrane as the electrolyte membrane, water is generated in the anode catalyst layer. Therefore, efficient drainage of this generated water is required, and improving the drainage capacity of the anode catalyst layer is necessary for performance improvement. By using the catalyst layer of this disclosure as the anode catalyst layer, the anode catalyst layer exhibits excellent drainage capacity and high conductivity, thereby improving the performance of the fuel cell cell.

Furthermore, since the embodiments described above are for illustrative purposes only, various modifications, substitutions, additions, and omissions may be made within the scope of the claims or their equivalents.

This disclosure provides a catalyst layer with excellent drainage properties and high conductivity, and is applicable to catalyst layers in fuel cells.

1 Electrolyte membrane 2a Anode 2c Cathode 3a Anode catalyst layer 3c Cathode catalyst layer 4a Anode gas diffusion layer 4c Cathode gas diffusion layer 5a Anode separator 5c Cathode separator 6 Electrolyte membrane-electrode assembly 7 Fuel cell cell 10a First conductive material 10b Second conductive material 11a First catalyst layer 11b Second catalyst layer 12 Catalyst 13 Ionomer 14 Mesoporous material 15 Mesopore

Claims (4)

A catalyst layer interposed between the gas diffusion layer and the electrolyte membrane of a fuel cell,
The catalyst layer comprises a first catalyst layer adjacent to the gas diffusion layer and a second catalyst layer adjacent to the electrolyte membrane.
The first catalyst layer and the second catalyst layer each include a first conductive material, a second conductive material having a smaller mode diameter than the first conductive material, and a catalyst supported on at least one of the first conductive material and the second conductive material.
The first catalyst layer has a smaller proportion of the weight of the second conductive material relative to the total weight of the first and second conductive materials compared to the second catalyst layer.
A catalyst layer characterized in that the mode diameter of the second conductive material is 22% or less of the mode diameter of the first conductive material . The invention further comprises an ionomer covering at least a portion of the first conductive material,
The first conductive material is a mesoporous material having mesopores with mode diameters of 1 to 50 nm inside,
The catalyst layer according to claim 1 , characterized in that at least a portion of the catalyst is supported in the mesopores. The catalyst layer according to claim 1 or 2 , characterized in that the second conductive material is a conductive carbon material. A fuel cell characterized in that the catalyst layer described in any one of claims 1 to 3 is used as the catalyst layer of the electrode on the side where water is generated during power generation.